The present invention relates to an actuator of a compact size with a built-in pilot valve for producing a relatively large operating force in a small range of working oil differential pressures.
Hydraulically operated acuators include double-acting cylinders for producing operating forces in opposite directions dependent on the difference between pressures acting on both ends of the piston. In such actuators, since mechanical frictional forces act on the cylinder itself and an external actuator mechanism, the operating force produced by the piston will be quite small when the differential pressure is relatively low, so that the actuator may operate slowly or fail to operate.
One solution would be to employ a servovalve for enabling the piston to generate a large operating force even in a small range of working oil differential pressures. However, the size of the actuator would be increased since the servovalve would be attached outside of the cylinder. If a pilot valve were used instead, a large operating force would be produced with a small differential pressure, but the actuator would be of a large size as the pilot valve would also be installed outside of the cylinder. Another problem would be that operation of the acutator might become unstable in some cases since a large operating force would be produced with a small differential pressure.